(1) Field of the Invention
The present invention relates to a butadiene based rubber composition having excellent resilience, fracture strength and wear resistance as a vulcanizate as well as excellent processability as an unvulcanizated rubber.
(2) Related Art Statement
Demands for low fuel consumption and safety in automobiles have recently been getting severer and severer, but conventional diene-based rubber materials do not satisfy both the characteristics of the low fuel consumption and the safety. Consequently, conjugated diene-based polymers having excellent resilience and fracture strength have been sought as tire rubber materials, particularly, rubber materials, such as, for tire treads.
Conventionally, as described in Japanese patent publication No. 4,996/69, U.S. Pat. No. 3,956,232, Japanese Patent Application Laid-open No. 205,414/82 and so on, these conjugated diene-based polymers have been obtained by polymerizing butadiene or copolymerizing butadiene with a vinyl aromatic compound such as styrene in a hydrocarbon solvent with use of an or9anic lithium initiator, and then reaching a resulting product with a halo9enated tin compound or an alkenyl tin compound.
However, since the above polymers have fracture strength, particularly poor fracture strength at high temperatures, they cannot satisfy severe performances required for the tire treads.
On the other hand, as rubber material having excellent fracture strength, there are natural rubber, synthetic polyisoprene rubber, etc., which are now widely and mainly used as tire treads for trucks and buses in service under a high load conditions. However, the above natural rubber and synthetic polyisoprene rubber have poorer resilience and wear resistance as compared with so-called lithium butadiene-based homopolymer (or copolymer) obtained by using the above organic lithium initiators. Consequently, improvement thereof has been strongly demanded.